This invention relates generally to heat removal and thermal dissipation in printed circuit (PC) boards and is more particularly directed to a mounting arrangement for securing a heat sink to a PC board in a positive locking manner.
Heat sinks are conventionally utilized with PC boards for limiting the operating temperature of electronic components positioned upon the board. The typical heat sink is comprised of a metal having a high thermal conductivity and is mounted to and in contact with the PC board to allow for the transfer of heat to the heat sink and its dissipation in the atmosphere. Heat sinks assume a wide range of configurations, all of which are intended to provide for secure mounting of the heat sink to the PC board, efficient heat transfer, and good thermal dissipation in the heat sink generally achieved by maximizing its surface area.
Referring to FIG. 1, there is shown a perspective view of a prior art heat sink 10. The prior art heat sink 10 is comprised of a heat conducting structure which includes a center portion 12 and a pair of lateral portions, each comprised of a plurality of spaced lateral ribs 16 integral with and extending from respective lateral edge portions of the aforementioned center portion. The heat sink 10 comprised of the center portion 12 and lateral ribs 16 is adapted for generally vertical positioning upon a PC board 18. The plurality of spaced lateral ribs 16 extending from the center portion 12 provide the heat sink 10 with a large surface area for more efficient heat removal from the PC board 18 and transmission to the surrounding environment by the heat sink. The center portion 12 of the heat sink 10 may be provided with an aperture 14 therein for directly mounting a circuit component (not shown) to the heat sink for limiting its operating temperature. The circuit board 18 is provided with a plurality of apertures 24, 26 and 28 which are adapted for receiving respective mounting tabs 20, 22 (a third aperture is not shown in FIG. 1) positioned on the lower edge portion of the heat sink 10. With a mounting tab inserted from above within each of the mounting apertures in the PC board, each of the mounting tabs is engaged from below the PC board and twisted about the longitudinal axis of the mounting tab so that the lateral edges of each mounting tab engage adjacent edges of the PC board which define the aperture within which the mounting tab is positioned. It is in this manner that the prior art heat sink 10 is positioned upon and secured to the PC board 18.
Because of the passive nature of the manner in which they function, the general simplicity of their design, and the availability of high heat conducting metals and alloys which can be readily shaped into heat sink structures, most limitations and problems encountered with heat sinks such as shown in FIG. 1 relate to the manner in which they are secured to the PC board. For example, a mounting arrangement which affords less than tight fitting, intimate contact between the heat sink and the PC board is limited in the amount of thermal energy which can be removed from the PC board and may result in malfunction or even destruction of circuit components positioned on the PC board substrate. The loose fitting positioning of the heat sink not only limits the amount of heat which can be dissipated, but also increases the likelihood of the heat sink becoming completely disengaged from the PC board and its removal therefrom, particularly where the PC board is subjected to vibration and shock. Removal of the heat sink from the PC board generally results in failure of the circuit mounted to the board because of the tight tolerances within which such circuits are designed. Finally, prior art heat sinks are generally secured to the PC board either by soldering the heat sink mounting tabs to the board or twisting the mounting tabs inserted within a PC board aperture so that the lateral edges of the mounting tabs engage and deform an adjacent edge of the PC board aperture. This mounting arrangement makes it difficult, if not impossible, to remove a heat sink once installed without either damaging the PC board or deforming the heat sink to the point where it is not re-usable.
The present invention represents an improved heat sink which does not suffer from the aforementioned limitations of the prior art in that it is easily inserted on a circuit board and maintained securely in position thereon by means of a positive locking force exerted by the mounting tabs thereof on the PC board. The extent of engagement between the heat sink and PC board may be fixed as desired during installation of the heat sink thereon in a mounting configuration which allows for easy removal of the heat sink from the PC board and its re-use.